As natural resources such as petroleum, coal, natural gas and the like are depleted together with development of industry and increase in population, a lot of studies on general wind turbines for generating electric energy using power of wind are under progress as an alternative energy source, and the range of use of the wind turbines is gradually expanded owing to low cost and eco-friendly reasons since the wind turbines use wind existing in the nature as an energy source.
A wind turbine of a prior art is described with reference to drawings.
Referring to FIG. 1, in a wind turbine 10 of the prior art, a blade 12 having a predetermined length is rotatably installed on the top of a high rising tower 11 built on the surface of the earth using a hub 14 as a medium. The hub 14 is connected to a nacelle 13, and the nacelle 13 is embedded with a gear box, a generator and a control device (not shown) inside thereof. In addition, the wind turbine 10 is configured such that rotating power of the blade 12 may reach the wind turbine 10 through the main shaft by way of the hub 14.
Referring to FIG. 2, the blade 12 obtains a three-dimensional shape by distributing a plurality of airfoil shapes in a span direction (length direction). It is general that a thick airfoil 12a is used toward the root of the blade 12 for structural stiffness and a thin airfoil having a superior lift-to-drag ratio (lift coefficient/drag coefficient) is used toward the tip of the blade 12.
Performance and efficiency of the wind turbine are determined by the shape of the airfoil configuring the cross section of the blade 12, and selecting an appropriate airfoil acts as a very important factor in a wind turbine operating for an extended period of time.
However, most of airfoils 12a currently used in a wind turbine are developed for airplanes, and taking for example the Reynolds number which is an important factor in fluid mechanics, the Reynolds number in an operating condition is about 6,000,000 in the case of an airplane, whereas it is only 500,000 to 1,600,000 in the case of a wind turbine, and thus there is a problem in that decrease in the performance of a wind turbine is induced if an airfoil used in a field of a completely different operating condition is used as a cross-sectional shape of the blade 11 of the wind turbine.
Furthermore, since the blade of a wind turbine is a large size having a span of ten meters or more and is not easy to clean although it is continuously exposed to contamination (dusts, dead bodies of insects, moisture, icing and the like), decrease in performance is expected due to the contamination.
Accordingly, a blade of further higher efficiency cannot be expected since an airfoil developed for airplanes is used as is without considering these effects of blade, and thus a countermeasure for this problem is required.